ASM Single Action Revolver .357 Magnum Compatibility & Safety

Question
I have an ASM ARMY single action revolver.  The barrel is marked 357 M.  I have fired 38 + P and its reliable and accurate.  Does the 357 M in the barrel indicate its a 357 Magnum and is it safe to shoot that load?

Answer
Although I do not have familiarity with that particular firearm, I do not know of any other cartridge that could be designated ".357 M" than the .357 Magnum. The .357 Magnum cartridge is 1/10 of an inch longer than the .38 Special. This was done deliberately so that the .357 cartridges could not fit into a gun chambered and rated for .38 Special.

I would take it to a gunstore and have them check it and tell you for sure, but if it is marked "357 M" and .357 Magnum cartridges will fit into it, I'm 99% sure that that is the cartridge it is chambered for.